IEC 60904-9:2020 is applicable for solar simulators used in PV test and calibration laboratories and in manufacturing lines of solar cells and PV modules. This document define classifications of solar simulators for use in indoor measurements of terrestrial photovoltaic devices. Solar simulators are classified as A+, A, B or C based on criteria of spectral distribution match, irradiance non-uniformity in the test plane and temporal instability of irradiance. This document provides the required methodologies for determining the classification of solar simulators in each of the categories. A solar simulator which does not meet the minimum requirements of class C cannot be classified according to this document. This document is used in combination with IEC TR 60904-14, which deals with best practice recommendations for production line measurements of single-junction PV module maximum power output and reporting at standard test conditions. This third edition cancels and replaces the second edition issued in 2007. This edition includes the following significant technical changes with respect to the previous edition: - Changed title; - Added spectral match classification in an extended wavelength range; - Introduction of new A+ class; - Definition of additional parameters for spectral irradiance evaluation; - Added apparatus sections for spectral irradiance measurement and spatial uniformity measurement; - Revised procedure for spectral match classification (minimum 4 measurement locations); - Revised measurement procedure for spatial uniformity of irradiance; - Added informative Annex for sensitivity analysis of spectral mismatch error related to solar simulator spectral irradiance.